This invention relates to a method and device for controlling a magnetic field of an electromagnet for a magnetron sputtering source.
A conventional magnetron sputtering apparatus is shown in FIG. 11. The apparatus shown in the figure is explained hereinbelow. The reference numeral 20 denotes a vacuum chamber in which are provided a gas introduction port 21 for introducing support gas (e.g., argon gas) and a gas exhaust port 22 to which a vacuum pump is connected for evacuating the vacuum chamber 20. In the interior of the vacuum chamber 20, there are opposingly provided an anode 24 on which substrates 23 are mounted, and a magnetron sputtering source 25. The magnetron sputtering source 25 is provided with an electromagnet 28 on the rear surface of a target 29, which also serves as a cathode. The electromagnet 28 comprises a central yoke 26b projecting upwards from the center of a plate-shaped bottom yoke 26a which is made of a ferromagnetic material of a wall-shaped peripheral yoke 26c projecting upwards from the periphery of the bottom yoke 26a and circularly enclosing the central yoke 26b, a central coil 27a wound around the central yoke 26b, an inner peripheral coil 27b wound around the inner periphery of the peripheral yoke 26c on the side of the central yoke 26b, and an outer peripheral coil 27c wound around the outer periphery of the peripheral yoke 26c.
The central coil 27a is formed by winding its coil around the central yoke 26b in the circumferential direction. The inner peripheral coil 27b and the outer peripheral coil 27c are formed by winding their coils around the peripheral yoke 26c in the circumferential direction.
In this sputtering apparatus, the vacuum chamber 20 is evacuated and then argon gas, for example, is introduced thereinto. Each of the coils 27a, 27b, 27c is charged with an electric current. At the same time, the target 29 is charged with an electric current, thereby starting the sputtering operation. With electric current flowing through each of the coils, the electromagnet 28 generates arched lines 30 of magnetic force which originate from the peripheral yoke 26c towards the central yoke 26b. Through the operation of the lines of magnetic force, the electrons generated by the electric discharge are restricted between the anode 24 and the target 29 to a space enclosed by the lines 30 of magnetic force and the target 29. The electrons collide with the molecules of the argon gas while making a cycloidal movement. The electrons will excite or ionize the argon gas, and thus generate plasma of high density in the space. Then, the ions in the plasma sputter the target 29 which is the cathode, and those particles of the target 29 which are generated by sputtering are caused to adhere to the substrates 23 to form thin films thereon.
Electric current is so controlled that constant amounts of current are made to flow in the same direction through the central coil 27a and the inner peripheral coil 27b, and that a constant amount of electric current is made to flow in a predetermined direction through the outer peripheral coil 27c.
In the conventional method of controlling the electromagnet for a magnetron sputtering source, as described above, constant amounts of electric current are controlled to flow through the central coil 27a and the inner peripheral coil in the same direction and a constant amount of electric current is made to flow through the outer peripheral coil 27c in a predetermined direction, and the shape of the arched lines 30 of magnetic force generated near the surface of the target 29 undergoes little or no change. Therefore, a plasma of high density concentrates on a spot where the lines 30 of magnetic force become parallel to the target 29, and that a small portion of the target which corresponds to the spot in question becomes eroded, resulting in disadvantages in that a wide area of the target 29 cannot be uniformly sputtered and that the utilization of the target 29 is poor.